A Systematic Literature Review of Nutrition Interventions Implemented to Address Food Insecurity as a Social Determinant of Health

Background: Policy initiatives have provided funding for non-acute nutrition interventions to address food insecurity as a social determinant of health, but more research is needed to understand the outcomes of these initiatives in order to determine the areas of highest impact. Therefore, the purpose of this systematic review was to evaluate the outcomes that were assessed in three nutrition interventions (produce prescription programs, medically tailored meals, and community supported agriculture) that aim to address food insecurity as a social determinant of health, and this was undertaken in order to identify future areas of study that can heighten impact. Methods: This systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) criteria. A list of search terms and keywords were compiled by the research team. A Boolean search was conducted from 1 January 2000 to 1 January 2023 in the PubMed advanced search database. Results: A total of 1015 articles were initially pulled from the PubMed database, and, after a screening process, 21 articles were included in our review. Nineteen of the articles focused on adult populations or families and two focused on children. The main outcomes assessed were changes in self-reported dietary intake, while a few of the articles addressed feasibility and cost-related outcomes. Conclusions: More research is needed to assess whether nutritional interventions to address food insecurity as a social determinant of health are feasible and more cost effective in the long term. Additionally, more work should be conducted in pediatric populations, which could have a robust return on investment in terms of both healthcare utilization and healthcare expenditure.


Introduction
In 2021, the United States Department of Agriculture (USDA) reported that 34 million people are food insecure in the United States [1]. A disproportionate number of children, single-parent households, racial/ethnic groups, and people from disadvantaged backgrounds suffer from low food security [1]. Food insecurity is associated with poor glycemic control [2], cardiometabolic diseases [3], and chronic disease [4]. The increase in the number of individuals with these conditions leads to higher healthcare utilization and higher spending and costs [5]. Due to the higher costs associated with food insecurity, Medicaid coverage has expanded in some states to include new and reformed nutrition services focused on alleviating food insecurity, which were not offered previously [6,7]. In particular, as a part of North Carolina's (NC) Medicaid transformation plan (prior to the passage of Medicaid expansion in March 2023), the Healthy Opportunities Pilots (HOPs) program was initiated in March 2022 [6,7]. The aim of the HOPs is to improve health outcomes related to social determinants of health (e.g., food insecurity), thereby lowering Medicaid expenditures due to improved outcomes [8]. Social determinants of health are "conditions in which people are born, grow, live, work and age" [9], and food insecurity is an example of a social determinant of health because it is "a household-level economic and social condition of limited or uncertain access to adequate food" [10].
As an example of how addressing food insecurity can lower healthcare utilization and costs, dietary intake, BMI, and diet-related health outcomes (such as blood pressure and cholesterol) are all linked to food insecurity, insofar as those who are food insecure often have worse dietary behaviors and, thus, have higher BMI and are at increased risk of high blood pressure and cholesterol [2][3][4]. Therefore, if food insecurity is reduced, dietary intake, BMI, and other related health outcomes should also decrease, and this would result in reductions in healthcare expenditure.
Specifically, the North Carolina HOPs target food insecurity through medically tailored meal delivery, healthy food boxes, produce prescription programs, nutrition and cooking coaching/counseling, and increased links to community-based food services [6,7]. However, the outcomes associated with these three strategies, which provide tangible food (medically tailored meal delivery, healthy food boxes/ community supported agriculture, and produce prescription programs), have not been systematically evaluated or compared. Thus, we selected these three interventions as the focus of the current systematic review. For the purposes of this review, a produce prescription program was defined as a program that is implemented to impact the dietary intake of fresh fruits and vegetables by providing prescriptions for them in the form of a voucher, cash, or an allotment of a card [11]. Programs that implement medically tailored meals are those that tailor specific, pre-packaged food in order to meet nutrients that are medically required in order to address certain chronic conditions through food [12]. Community-supported agriculture (CSA) is a type of direct-to-consumer marketing that is a partnership between local farms and customers ("members"), who purchase a CSA share in return for regular food deliveries from that farm. The food and the farm thereby become tied to the community, where mutual care of the land is distributed, and where the goods that are gathered are shared [13].
In addition to the North Carolina HOPs, the USDA has authorized the creation of the Gus Schumacher Nutrition Incentive Program (GusNIP), which was formerly known as the "Food Insecurity Nutrition Incentive Program [11]. The GusNIP provides funding for eligible organizations which implement and evaluate projects that provide incentives to low-income participants in order to increase their purchase of fruits and vegetables, which they do through nutrition incentive programs and produce prescription programs. Thus, the purpose of our systematic review was to evaluate the outcomes that have previously been assessed for these specific nutrition interventions, and the focus was on the North Carolina HOPs (medically tailored meal delivery, healthy food boxes/ community supported agriculture, and produce prescription programs) that aim to address food insecurity as a social determinant of health. The goal of our paper is to identify future areas of study in order to heighten the impact of HOPs.

Materials and Methods
Literature search strategy: This systematic literature review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [12,14]. A Boolean search was developed in Medline via the PubMed interface by librarian HR in consultation with KN, using keywords related to food insecurity, cardiometabolic diseases, nutrition interventions, and study types. No publication date filter was used, and the search was run from inception to January 2023, with 1015 results. The full search strategy can be seen in the ECU institutional repository entry at http://hdl.handle.net/10342/12701 (accessed on 4 May 2023). A total of 1015 articles were screened based on the inclusion and exclusion criteria described below.
Inclusion and exclusion criteria: The focus of this review was peer-reviewed publications that focused on the effectiveness of three specific non-clinical food interventions on food insecurity or chronic conditions. Dissertations, white papers, review articles, and abstract-only papers were excluded. This review used only quantitative results as the primary outcome measure. The articles included had to have a population from a developed country. Study outcomes had to include either dietary outcomes, such as increased intake of fruits and vegetables or whole grains, or food insecurity, body mass index, health-related outcomes (such as improvement in HbA1c levels in diabetic participants, blood pressure levels in hypertensive participants), feasibility outcomes, or cost-related outcomes. The papers included had to have recruited and reported on data collected from participants from a public health system or a health care system. Data Extraction and Analysis: Using Covidence, (https://www.covidence.org/, access on 8 May 2023) an online screening operator tool, a title and abstract screening was performed first (BernardDeckerPublicLibraries.edu, 2023). The primary author screened the initial 1015 initial articles (See Figure 1). After the first screening, 914 articles were deemed irrelevant to the primary focus of this review. Independently, a two-author screening was conducted for the full-text screening portion of the remaining 101 articles. All of the conflicts were resolved during a designated meeting between the primary and secondary author. A total of 27 articles were selected for the extraction screen. During extraction, 6 articles were additionally excluded for inclusion in the final qualitative synthesis as they were found to not be directly linked with a health clinic or a health department as the referring entity for program participants. The following information was extracted: setting, length of study, type of study, number of participants, eligibility criteria, program type, dosage, and population demographic characteristics (e.g., mean age, race/ethnicity, socioeconomic status). The following outcomes were extracted: changes in BMI, dietary intake, food insecurity, condition improvements, feasibility, and cost-related outcomes. For the purpose of this review, feasibility refers to retention rates in the studies, successful attendance at nutrition education sessions (if applicable), redemption rates for vouchers (if applicable), and overall ease of use for participants. Cost-related outcomes could refer to cost effectiveness, the dollar amount per outcome achieved, or cost savings. The authors of the study used SNAP-Ed's definition of direct nutrition education. Indirect nutrition education [15], defined as "the distribution or display of information and resources, including any mass communications, public events (such as health fairs), and materials distribution, which involve no participation interaction with an instructor or multimedia", was not considered as nutrition education. Additionally, following SNAP-Ed definitions and guidelines, the study's authors did not include diabetes self-management education (DSME) as nutrition education, since nutrition education focuses on the prevention diet-related chronic diseases whilst DSME focuses on managing an already diagnosed condition.  Table 1 shows an overview of the included studies, and Table 2 provides more details on all of the studies included. A total of 21 studies were reviewed, including 13 (61.9%) food or produce prescription program studies [16][17][18][19][20][21][22][23][24][25][26][27][28][29], 4 (19.0%) medically tailored meal (MTM) program studies [5,[30][31][32], and 4 (19.0%) community-supported agriculture (CSA) studies [33][34][35]. Fifteen studies (71.4%) focused on adult populations and four (19.0%) focused primarily focused on families and pediatric populations. Only two (9.5%) of the studies focused on children. Nineteen (90.5%) of the articles were implemented in the United States in various states, and the remaining two studies were implemented in Canada and Australia. Over half of the study designs (n = 13, 61.9%) were quasi-experimental with a pre-post design, while only two (9.5%) were randomized controlled trials. Additionally, eight of the studies (38.1%) provided direct nutrition education to their participants, although one study specifically noted the lack of attendance at classes due to accessibility issues [33].   Table 1 shows an overview of the included studies, and Table 2 provides more details on all of the studies included. A total of 21 studies were reviewed, including 13 (61.9%) food or produce prescription program studies [16][17][18][19][20][21][22][23][24][25][26][27][28][29], 4 (19.0%) medically tailored meal (MTM) program studies [5,[30][31][32], and 4 (19.0%) community-supported agriculture (CSA) studies [33][34][35]. Fifteen studies (71.4%) focused on adult populations and four (19.0%) focused primarily focused on families and pediatric populations. Only two (9.5%) of the studies focused on children. Nineteen (90.5%) of the articles were implemented in the United States in various states, and the remaining two studies were implemented in Canada and Australia. Over half of the study designs (n = 13, 61.9%) were quasiexperimental with a pre-post design, while only two (9.5%) were randomized controlled trials. Additionally, eight of the studies (38.1%) provided direct nutrition education to their participants, although one study specifically noted the lack of attendance at classes due to accessibility issues [33]. The demographics of the sample populations varied, but the populations generally included a racially and ethnically diverse sample. Additionally, 16 of the studies had a majority female participant population, while 3 did not report the gender of the participants. Fourteen of the studies required that study participants were food insecure, uninsured, or using some type of federal food assistance program, such as SNAP or WIC, in order to be eligible to participate. A total of 15 of the 21 studies required that program participants be diagnosed with at least one chronic condition or be at risk of a chronic condition in order to be eligible to participate. The chronic conditions that participants had to be diagnosed with or at risk of consisted of prediabetes, type 2 diabetes, a cardiometabolic disorder, or being overweight/obese.
A total of 14 out of the 21 studies measured other health condition improvements, ranging from hemoglobin A1c, hypertension, waist circumference, mental and physical health, cholesterol, and diabetes management. The results for these outcomes were mixed, and most were not statistically significant. However, four studies found reductions in blood pressure [18,22,29,35], four found decreases in hemoglobin A1c [22,26,31,33], two found reductions in waist circumference [22,29], and one found improvements in cholesterol [27]. In terms of feasibility, 12 of the studies examined aspects of feasibility [16][17][18][19]24,26,27,[31][32][33][34][35] using the main measurements of redemption or distribution rates, adherence to nutrition education when offered, food waste, and participant satisfaction. For studies that tracked cost-related outcomes [5,16,26,27], these included cost per redemption, total cost distributed to participants, avoided produce costs to participants, and estimated reduction in medical costs per month.

Discussion
In this literature review, we examined the outcomes that have been assessed in three specific nutrition interventions, all of which aimed to address food insecurity as a social determinant of health in order to identify the areas of improvement that are needed to advance the field (n = 21 studies). The majority of papers included in this comprehensive literature review are produce or food prescription programs (n = 13, 61.9%). There should be more studies dedicated toward evaluating the effectiveness of MTMs, CSAs, and other non-clinically based nutrition interventions. In addition, most of the studies were focused on adult populations, and more work is needed in pediatric populations as children have not already developed chronic diseases, and, moreover, intervening among children would probably also provide a robust return on investment. When children have healthy habits and can maintain those habits throughout their lifespan [36], this will likely decrease healthcare utilization and expenditure related to chronic disease management among older adult populations.
The majority of studies utilized a quasi-experimental pre-post design. There should be additional studies using randomized controlled trials as the study design. There are qualified, dedicated health departments or federally qualified health centers that could be tested as potential referring entities, and this would open more intervention availability among many communities. Eight studies included a nutrition education component. In some cases, these nutrition education sessions were poorly attended and under-utilized. More work is needed to encourage participation in nutrition education sessions so that participants can increase their knowledge and confidence regarding how to use provided produce.
Overall, the most frequently measured outcome was changes in dietary intake among the study participants. The second most frequently measured outcome was status changes regarding food security. Because the three interventions examined in this review have the ultimate goal of reducing food insecurity and improving nutrition security, future evaluations of similar interventions should include a measure of food insecurity and nutrition security outcomes. Furthermore, only one study included in this review [27] used objective measures of dietary intake. Future studies should evaluate the impact of these three nutrition interventions on objective measures of diet, which are not subject to recall biases and social desirability [37].
One outcome that was used to assess feasibility was a measure of redemption rate, but redemption rates were measured differently across the articles. For example, Abel et al. [17] examined the total number of vouchers redeemed divided by the total number of vouchers distributed, while Aiyer et al. [16] examined the average number of prescriptions redeemed per participant and the mean number of times the prescriptions were redeemed. Additional studies could determine the most salient measures of redemption rates in order to ensure that future studies define redemption rates similarly across studies.
Other reviews have been conducted in order to assess how clinics or healthcare organizations are offering access to healthy foods. In one review paper written by Veldheer et al., 8876 articles were screened and a total of 44 manuscripts were retained for inclusion in their review [38]. The review by Veldheer et al. utilized only papers that were clinic-based, whereas this current review included articles in both a clinical and community health center. The inclusion of public health departments or centers could possibly have provided a better overview of the population for each particular area due to more marginalized and disadvantaged populations receiving care at community health sites. Veldheer et al. did not assess whether the studies were cost effective or the feasibility of the studies that were included [38]. It is important to assess cost benefits from each study so that input versus output spending can be analyzed, replicated, and improved.
Bhat et al. [39] conducted a meta-analysis to examine healthy food prescription programs and their impact on dietary behaviors, BMI, systolic and diastolic blood pressure, HbA1c, and blood lipids. They found a 22% increase in FV intake, a BMI decrease of 0.6 kg/m 2 , and a HbA1c decrease of 0.8% [39]. Bhat et al. also noted the need for large, randomized controlled trials to examine the efficacy of healthy food prescription programs [39].
Currently, 41 states have adopted Medicaid expansion [40]. Some states, such as North Carolina, have begun implementing and evaluating programs that have the potential to reduce healthcare costs. The results of Medicaid expansion programs, such as PPP, MTM, and CSAs, will lend insight into whether these programs improve diet, overall health and well-being, and healthcare cost savings, thereby reducing hospital readmission rates and also reducing dependency on the use of emergency services. If the results of these evaluations are promising, Medicaid and other insurance companies could benefit from investing in food delivery programs due to their ability to reduce healthcare expenditure. While this review demonstrated that few papers evaluated cost-related outcome data (healthcare expenditures), this may be due to the complexities of measurement. Since private and public insurance companies negotiate pricing with healthcare organizations, it is difficult to quantify healthcare expenditures, especially when examining costs across different healthcare entities and different geographic regions/states. Therefore, going forward, having a more straightforward measure of healthcare utilization may be more insightful for researchers who examine the cost effectiveness of food programs.
The USDA authorized GusNIP provides funding to provide incentives to low-income participants through nutrition incentive programs and produce prescription programs. While data from some of these projects have been evaluated, others are currently being evaluated in order to assess feasibility, diet-related outcomes, and reduction in healthcare utilization. This systematic literature review can help inform future GusNIP request for applications or even provide information for potential grantees on lessons learned and what has been most effective to date. This paper has both strengths and limitations. One strength is that two independent authors screened full-text articles and extracted data from all of the included papers. Discrepancies were discussed at a designated time between the two authors, and a consensus was reached regarding each paper or disagreement. A librarian was consulted with in order conduct the Boolean search from PubMed advanced database. However, there are some limitations to this review. The PubMed database was the only search engine used in this literature review, and more search engines could have yielded more or different results. Additionally, the primary author screened titles and abstracts, but for more validated results, the two independent authors could both have screened all items from the beginning of the process. Furthermore, there was no formal definition of developed countries, and, thus, some papers could have been inadvertently not included. Two of the included articles [16,23] were food vs. produce prescription programs, but we included these due to their specific focus on produce when describing the intervention. In the future, it will be important to compare the outcomes of food versus produce prescription programs. Lastly, a quality assessment of each article was not conducted by the authors.

Conclusions
To inform evidence-based policy supporting funding for nutrition interventions to address food insecurity as a social determinant of health, more research is still needed. Few of the studies examined in the current review included any cost-related outcomes. Thus, there need to be more studies analyzing the cost effectiveness of interventions to address food security as a social determinant of health. Since GusNIP has been funding nutrition incentive programs, we hope that grantees will continue to publish their results. More specifically, in the 2018 farm bill, GusNIP changed its focus to also include healthcare costs and utilization rates. However, this data has been difficult to evaluate. Going forward, there should be clear distinctions between the average cost of an acute care stay or medical visit tailored for chronic conditions and food insecurity compared to the cost-benefit analysis of these non-acute care-based nutrition interventions. In the same capacity, studies that show feasibility will only encourage replication in more areas where the services are needed.
Overall, there were many positive results of these nutrition interventions, and they should result in reductions in healthcare costs and improved population health. If additional studies are conducted and demonstrate similar positive results in terms of health outcomes and cost reductions, additional investments in these programs will be warranted.